Filter underdrain



June 13, 1944. E. w, WELP 2,351,308

FILTER U1-1DERDRAINy Filed March 1, 1943 22 l'iig. mm

- "lNvENTbR' EDWARD W, WELP A ATTORNEY Patented June 13, 1944 FILTER .UNDERDRAIN j y Edward W. Welp, Chicago, Ill., assignor to Graver Tank & Mfg. Co., Inc., a corporation of Dela- Ware Y Application March 1, 194e', serial No. 477,670

claims. (ci. 21o-124) This invention relates to apparatus of the filter type, and particularly such apparatus the major portion of which is constructed from wood staves held together by hoops.

Filter tanks of wood are well known to the art, but difficulties came up, especially in connection with the underdrains. Other lter tanks, constructed from steel, were highly successful. A most'eicient underdrain in steel tanks consists of a fiat steel plate, welded to the steel shell around the periphery and having numerous strainer ttings with small openings distributed over thev surface of said plate. `.A bed of gravel is ordinarily placed on top of such a plate. The, lteringmaterial, such as sand, anthracite, zeolite, or the like, is, supported lby the gravel. The distribution of backwash water, as well as the taking up of water in downward filtration, in the brlning and rinsing of zeolite filters, and so on, is satisfactorily realized by means of said underdrain construction, which at the same time is extremely durable and inexpensive. Other constructions, such as pipes installed above the bottom, give rise to various diiliculties, due to accumulation of stagnant water or brine below the pipes, and the like.

The main object of this invention is to make the desirable features of said steel tank underdrain available to, wood tanks. The diiliculty is that in the making of wood tanks the shape 'and size of the wall portion of the tank .is subject to change, and the simple and ecient welding of the plate to the wall is out of question, The staves for the wood wall are initially shaped, set up, and tied together by the hoops, so that the inner edges of the staves are in contact and compression. The st-aves are then moistened and caused to swell, with the hoops tightened. Incident to this process the precise shape of the inner side of the wall, or series of staves, is subject to some change, due to compression and distortion of the staves. Additional irregularities are sometimes caused by the swelling of planks in the bottom of the tank. These changes and irregularities are of minor proportion as compared with the area of the tank, but are quite considerable in relation to the size of the strainer orices provided in said steel plates. As a result, suchsteel plates when heretofore installed in wood tanks,

allowed the backwash waterto escape Vin great .50

amounts around the periphery, reducing the amount distributed throughl the central portion of the underdrain, and reducing the eiciency of the backwash.

It is a further object of my invention 'to pro- 55 'the aid of standard tools. A certain clearance vide apparatus which is free from said defects and shortcomings of prior art devices.

' Other objects may appear from the following disclosure.

In the drawing Figure 1 is a front elevation of apparatus according to this invention.

Figure 2 is an enlarged front elevation, partly in section, ofV a detail from Figure 1.

Figure 3 isa similar view of a modified detail.

Figure lisa plan view of the detail of Figure 3.

Figure 5v is a still more enlarged elevation, partly in section, yof a detail from Figure 2. Y The inventionis illustrated by a zeolite softener I0, although it is applicable to other devices of the iilter type also. The softener has a substantially cylindrical side wall II composed ofY a se-v ries of wood stavesA I2 which are properly shaped and bevelled, and held together by hoops I3. A substantially circular bottom :I4 is held in an annular groove, I5 in the bottom party of the series of staves, closingthe tank at its underside. A round'kand dat steel plate I6 is disposed in thetank concentrically with vrespect to the .Wall I`I and bottom I4 and spaced above said bottom. This plate is heldy in the. aforesaid position by means Yof a substantially cylindrical steel ring I1 conc'entrically welded to the outer part of the plate, an annularly bent L-beam I8 welded to the ring I1, and bolts I9 holdingv this L.beamV I8 to the bottom'l. A

' The plate I 6 has regularly 'distributed over most of itssurface, small fittings 20 which are preferably made of stainless steel, so `that no corrosion may occur when water, salt-brine, or Various ,othermaterials contact the plate I6 and fittings 20L Each .tting 20 is screwed into a tapped hole 2I of the plateIB by means of a pipe thread `22 on the fitting. Each tting has a relativelylarge blind hole 23 drilled into its underside and ending short of the top, and a plurality of small drill holes'24 drilled into or through the sides of the iitting and establishing horizontal connections between the large hole 23 and the n outside. Thesehorizontal passages are located a short distance above the plate I 6 and cause a most desirable flow of'i'luid in the bafckwash of the lter, Vas well as incident to downward filter ing,` briningf,jrinsing,.and so on.

4The plate It is somewhat smaller than the inside of thewall II isreither` during or after the makingv'and startingotthe filter tank. Thus the plate-I6 -and the bolting-down ring I8 are easily inserted injthe'iwoodtank, and bolted down with substantially, said annular zone around said steel ring.

3. Apparatus according to claim 1 wherein said seal and support ring comprises a ring of seal material disposed in said annular zone, and said 5 plate has a peripheral part extending over an inner part of said ring of seal material.

4. Apparatus according to claim 1 comprising a plurality of strainer fittings made of stainless steel, regularly distributed over said major part o1' said plate, and screwed into said plate, each l0 of said ring of wood.

EDWARD W. WELP. 

